Method of making a composite heavy duty bushing

ABSTRACT

A COMPOSITE HEAVY-DUTY BUSHING, SUCH AS A BEARING BUSHING OR BEARING RACE (FIG. 4) CONSISTS OF A HIGH LOADBEARING OR WORKING PORTION CONSISTING OF SLEEVE COMPOSED OF SINTERED POWDERED HIGH-PERFORMANCE ALLOY SUCH AS A MANGENESE-MOLYBDENUM IRON ALLOY AND A SUPPORTING OR MOUNTING SLEEVE SUBJECTED TO LESS CONCENTRATED OR INTENSE LOADS MADE OF A LOWER-PERFORMANCE LIGHTER-DUTY INEXPENSIVE FERROUS BASE METAL, SUCH AS SINTERED POWDERED IRON. THESE TWO SLEEVES ARE SEPARATELY BRIQUETTED, AND THEN ASSEMBLED TELESCOPICALLY. THIS ASSEMBLY IS THEN SINTERED WHILE THE SLEEVES ARE THUS UNITED, AND FINALLY HOT-FORGED IN AN AXIAL DIRECTION. THIS FORGING OPERATION DESIFIES THE COMPOSITE ASSEMBLY FROM THE SINTERED BRIQUETTE DENSITY OF ABOUT 75% TO A FINAL DENSITY OF ABOUT 98% AND AT THE SAME TIME UPSETS THE ENDS OF THE BASE METAL SLEEVE INTO AN ADJACENT END BEVEL IN THE HIGH PERFORMANCE ALLOY SLEEVE, THEREBY CLINCHING THE TWO SLEEVES INSEPARABLY TO ONE ANOTHER. PHOTOMICROGRAPHS OF LONGITUDINAL SECTIONS OF THESE COMPOSITE BUSHINGS SPANNING THE JOINT BETWEEN THE TWO SLEEVES (FIG. 7) AFTER SUBSEQUENT CARBURIZING AND HARDENING HEAT TREATMENT SHOW A SUPERIOR INTERLOCK THEREBETWEEN RESULTING FROM A MIGRATION OF THE METALS INTO ONE ANOTHER ACROSS THE INTERFACE THEREBETWEEN. TORSION TESTS PERFORMED ON SUCH SECTIONS SHOW ADEQUATE STRENGTHS WITHOUT FAILURE ALONG THE JUNCTION SURFACES WHICH COMPARE FAVORABLY WITH THE STRENGTH OF SIMILAR SINGLE SOLID METAL BUSHINGS. THESE PHOTOMICROGRAPHS ALSO SHOW THAT SUCH A COMPLETE BOND HAS BEEN ACHIEVED ALONG THE CENTRAL OR AXIAL PORTION OF THE JOINT, THAT THE BEVELING OF THE ENDS IS NOT ESSENTIAL IN ORDER TO FORM A JOINT OF ADEQUATE STRENGTH. SUCH BEVELING AT THE ENDS IS THEREFORE OPTIONAL AND IS PROVIDED AS AN ADDITIONAL MEANS OF RETENTION OF THE INNER SLEEVE INSIDE THE OUTER SLEEVE.

W.YM.DUNN 3,761,257

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INA/ER SL 65 V5 SLEEVE BRIQUETTE 0 3 e 9 H 2 I 2 E a G HR w 2 Wm r a 2 a 5 @v vvv vw m 5 6 5 w \v W. M. DUNN Sept. 25, 1973 METHOD OF MAKING A COMPOSITE HEAVY-DUTY BUSHING 2 Sheets-Sheet 2 Original Filed June-l4, 1971 FIG United States Patent Int. Cl. 1322f 7/02 US. Cl. 75.208 R 7 Claims ABSTRACT OF THE DISCLOSURE A composite heavy-duty bushing, such as a bearing bushing or bearing race (FIG. 4) consists of a high loadbearing or working portion consisting of a sleeve composed of sintered powdered high-performance alloy such as a manganese-molybdenum iron alloy and a supporting or mounting sleeve subjected to less concentrated or intense loads made of a lower-performance lighter-duty inexpensive ferrous base metal, such as sintered powdered iron. These two sleeves are separately briquetted, and then assembled telescopically. This assembly is then sintered while the sleeves are thus united, and finally hot-forged in an axial direction. This forging operation densifies the composite assembly from the sintered briquette density of about 75% to a final density of about 98% and at the same time upsets the ends of the base metal sleeve into an adjacent end bevel in the high performance alloy sleeve, thereby clinching the two sleeves inseparably to one another. Photomicrographs of longitudinal sections of these composite bushings spanning the joint between the two sleeves (FIG. 7) after subsequent carburizing and hardening heat treatment show a superior interlock therebetween resulting from a migration of the metals into one another across the interface therebetween. Torsion tests performed on such sections show adequate strengths without failure along the junction surfaces which compare favorably with the strength of similar single solid metal bushings. These photomicrographs also show that such a complete bond has been achieved along the central or axial portion of the joint, that the beveling of the ends is not essential in order to form a joint of adequate strength. Such beveling at the ends is therefore optional and is provided as an additional means of retention of the inner sleeve inside the outer sleeve.

This is a division of our co-pending application, Ser. No. 152,860, filed June 14, 1971, for Composite Heavy- Duty Bushing and Method of Making the Same.

In the drawings:

FIG. 1 is a longitudinal section through the outer powdered metal sleeve of the present composite bushing, after briquetting but before sintering, according to one form of the invention;

FIG. 2 is a similar longitudinal section through the inner powdered metal sleeve of the present composite bushing, after briquetting but before sintering, according to the same form of the invention;

FIG. 6 is a flow diagram of the steps involved in the method of making the composite bushing of FIG. 4; and

FIG. 7 is a photomicrograph of a longitudinal section of the composite bushing of FIG. 4, showing the interlocking and interfiow of the different metals at the interface.

Referring to the drawings in detail, FIG. 4 shows a composite heavy-duty bushing, generally designated 10, according to one form of the invention, as composed of a high performance alloy outer sleeve 12 joined at a generally cylindrical interface indicated by the dotted line 14 to a base metal inner sleeve 16, with opposite end portions 18 of the base metal sleeve 16 expanded into engagement with internal bevels 20 in the outer sleeve 12. The composite bushing 10 has flat annular opposite end surfaces and an internal bore 24. Where the outer sleeve 12 of the composite bushing 10 is to constitute the heavy-duty loadbearing component (FIG. 4), it is formed from highperformance alloy powder, such as of the composition set forth below, whereas the less intense load-bearing inner sleeve 16 is suitably formed from powdered iron, thereby producing a composite heavy-duty bushing 10 suitable, for example, for the inner race of a roller bearing.

On the other hand, if the composite heavy duty bushing is to be a bearing bushing 30 for rotatably supporting a shaft in its bore 32, or the outer race of a roller bearing, the inner sleeve 36 is composed of the high performance alloy and the outer sleeve 34 of the powdered iron (FIG. 5), with a similar generally cylindrical interface 38 having opposite end portions 40 expanded inward against external bevels 42 at the opposite ends of the inner high performance alloy sleeve portion 36. The composite bushing 30 of FIG. 5 has flat annular opposite end surfaces 44.

The sleeves l2 and 16 are formed from powdered metal briquettes 46 and 48 (FIGS. 1 and 2) which are formed by briquetting suitable high performance alloy powder and iron powder respectively in the correspondinglyshaped die cavities of conventional briquetting presses (not shown), the said die cavities being formed between a die with a cylindrical die bore, a cylindrical core rod, and upper and lower punches, by briquetting procedures well known to those skilled in the powder metallurgy art. The upper and lower punches of the briquetting press used for producing the outer high performance alloy sleeve 46 have bevels on the ends thereof adapted to produce corresponding end bevels 50 which extend axially toward one another from the flat end portions 52 (FIG. 1). The cylindrical bore of the briquetting press die forms the outer cylindrical surface 54 of the briquette 46 whereas the core rod thereof forms the cylindrical inner surface 56. The die for briquetting the inner sleeve 48, on the other hand, has upper and lower tubular punches with flat ends producing the flat upper and lower ends 58 of the inner sleeve briquette 48 whereas the cylindrical die bore and cylindrical core rod produce the cylindrical outer and inner surfaces 60 and 62 thereof respectively. The outer sleeve briquette 46 is formed (FIG. 6) by briquetting a powder of a suitable high performance metal or metal alloy, for example the so-called S.A.E. 4600 alloy powder. The inner sleeve briquette 48, on the other hand, by not requiring the heavy load-sustaining properties of the outer portion 12 of the composite bushing 10, is formed from iron powder.

The briquettes 46 and 48 are next assembled in telescoped relationship (FIG. 6) with an annular clearance of V-shaped cross-section therebetween at the opposite ends thereof (FIG. 3) and sintered in a conventional sintering oven at the customary temperatures, thereby forming a sintered composite sleeve 64 (FIG. 3). The composite sintered powdered metal sleeve 64 is then heated to a temperature preferably between 1500 F.

and 2100 F. and placed in the cylindrical bore 66 of the die plate 68 of a die set 70 mounted in a conventional hot forging press 72 (FIG. 3). The die set 70 includes the die plate 68 containing the cylindrical die bore 66, an upper tubular punch 74 with a cylindrical outer surface 75 telescoping with the die bore 66 and having a flat annular lower end face '76 surrounding a bore 78 telescoping with a cylindrical core rod 80. Also telescoping with the die bore 66 and core rod 80 are the outer and inner cylindrical surfaces 84 and 86 of a lower tubular punch 88.

In the carrying out of the method (FIG. 6) of making the composite heavy duty bushing 10 of FIG. 4, the upper punch 74 is retracted upward, whereupon the composite sintered powdered metal bushing 64 having a density of approximately 75% in its heated condition is placed within the die cavity 90 formed between the die bore 66, the core rod 80, and the upper and lower tubular punches 74 and 88, resting upon the annular upper end surface 92 of the lower tubular punch 88. The upper punch 72 is then moved downward into the die bore 66 and its lower end surface 76 caused to exert heavy deforming pressure upon the composite sintered powdered metal bushing 64. The upper end surface 92 of the lower tubular punch 88 acts as an anvil while the cylindrical surfaces 66 and 86 of the die plate 68 and core rod 80 prevent lateral flow of the metal. As a result, this hot forging operation (FIG. 6) is caarried out with sufficient force to compress the composite sintered powdered metal bushing 64 axially while at the same time causing its opposite ends 58 of its inner component 48 to be upset and expanded outward into the space provided by the bevel 50 on the outer component 46. At the same time, the hot forging pressure raises the density of the sintered powdered metal composite bushing 64 from approximately 75% to about 98%, so that it becomes substantially solid metal and presents the final appearance shown in FIG. 4. The forging pressure combined with the heat of forging, results in an excellent and continuous welding junction at the interface 14 between the cylindrical surfaces 56 and 62 of the outer and inner sleeves 46 and 48 and produces a migration of the metals of the outer and inner portions, now 12 and 16, thereacross. This results in an inseparable and continuous interlocking thereof along the inner face 14, as shown by the photomicrograph (FIG. 7), wherein the light-colored portion is the heavy-duty alloy and the dark-colored portions the iron.

The production of the composite heavy-duty bushing 30 of FIG. follows the same procedure as has been described above for the composite bushing of FIG. 4, except that the heavy duty alloy sleeve 36 is now inside and the low performance metal sleeve 34 is on the outside. The method constituting the separate briquetting of the inner and outer sleeves 36 and 34, their assembling telescopically, their sintering in assembled relationship and their forging also follows the procedure set forth in the flow chart shown in FIG. 6. In forging, as before, the metal at the opposite ends flows laterally against the bevels 42, thereby upsetting the opposite ends and clinching the bushings into an inseparable condition. It will of course be understood that the word iron as used herein includes iron having carbon therein for imparting the desired hardness as achieved by conventional heat treatment. It also includes conventional carburization of the iron for providing a hardened external surface.

The above-mentioned nickel-content S.A.E. 4600 iron alloy powder has the following composition:

Percent Manganese 0.20 Nickel 1.75 Molybdenum 0.25

with the remainder iron, plus carbon to suit.

The nickel-free high-performance iron alloy powder also mentioned above has the following composition:

with the remainder iron, plus high carbon 0.59% or low carbon 0.28%.

Heat treatment of the composite bushing 10 or 30 is carried out in the usual and customary manner.

While the above-described high performance iron alloy powders have been found useful and desirable in making the composite heavy-duty bushing of the present invention, it will be understood that other suitable highperformance alloy powders may also be used for the heavy-duty alloy sleeve 36.

The bevel 50 of FIGS. 1 and 3 which after forging becomes the bevel 20 of FIG. 4 and the bevel 42 of FIG. 5 provide an effective additional clinching of the inner and outer components 12 and 16 (FIG. 4) or 34 and 36 (FIG. 5). It has been found by actual tests, however, that the forging operation which results in the composite heavyduty bushing 10 of FIG. 4 and 30 of FIG. 5 effects such an interlocking action at the respective interfaces 14 and 38 by the migration of the component materials across the interface that the above-mentioned bevels are not indispensable to prevent separation of the outer and inner component bushings but provide an additional safeguard therefor under the application of extremely heavy loads. This interlocking by migration of the metals across the respective interfaces 14 or 38 is clearly shown in the photomicrograph (FIG. 7).

I claim:

l. A method of making a composite high-strength bushing comprising forming an inner briquette of powdered metallic material with a generally cylindrical outer junction surface thereon,

forming an outer briquette of powdered metallic material with a generally cylindrical inner junction surface configured and adapted to telescopingly engage said outer junction surface of said inner briquette,

at least one of said briquettes being composed of a high-performance heavy-duty manganese-molybdenum iron alloy and the other briquette being composed of a lower-performance lighter-duty ferrous base metal, moving said junction surfaces of said outer and inner briquettes into telescoping engagement with one another so as to form a composite briquette sintering said composite briquette into a sintered composite body having inner and outer sintered components corresponding to said inner and outer briquettes with corresponding junction surfaces therebetween,

heating said sintered composite body to a suitable hotforging temperature,

applying longitudinal hot-forging densifying pressure to said sintered composite body while restraining the outermost and innermost surfaces thereof from lateral deformation,

and thereby simultaneously forcing the adjacent portions of said inner and outer components of said composite briquette into interlocking engagement with one another with migration of material from at least one of said components into the other component across said junction surfaces between said components.

2. A method of making a composite high-strength bushing, according to claim ll, also including in the forming of said inner and outer briquettes the forming of a generally cylindrical outer surface on the outer briquette and a generally cylindrical inner surface on the inner briquette.

3. A method, according to claim 1, wherein said highperformance heavy-duty alloy is a nickel-free manganesemolybdenum iron alloy.

4. A method, according to claim 1, wherein said highperformance heavy-duty alloy is a nickel-content manganese-molybdenum iron alloy.

5. A method, according to claim 1, wherein the outer briquette is formed from said high-performance heavyduty alloy.

6. A method, according to claim 1, wherein the inner briquette is formed from said high-performance heavyduty alloy.

7. A method, according to claim 1, wherein the forming of said briquettes includes the providing of a clearance space directed laterally away from at least one end of the junction surface of one of said components and wherein the applying of said longitudinal hot-forging densifying pressure deforms the end portion of the other component laterally into said clearance space.

References Cited CARL D. QUAKFORTH, Primary Examiner B. HUNT, Assistant Examiner US. Cl. X.R.

29-4205; 75200, 226; 308- 237, 239, DIG. 5 

